This application is based on and claims priority to Japanese Patent Application No. 2000-278647, filed Sep. 13, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates generally to a water cooling system for an engine, and more particularly to an improved water cooling system that includes a pressure control valve.
2. Description of Related Art
During operation, typical internal combustion engines generate substantial heat and require that generated heat to be removed to avoid overheating. A number of cooling systems are available for that purpose. Typically, marine engines, such as, for example, outboard motors and inboard/outboard motors, employ an open-loop type water cooling system such that introduces cooling water from the body of water surrounding the motor and discharges the water to a location outside of the motor after the water absorbs some of the heat from the engine.
An outboard motor, in general, comprises a housing unit mounted on an associated watercraft by a bracket assembly and an engine mounted within the housing unit. The engine can employ an open-loop type water cooling system such as that described above. The housing unit normally defines a water supply passage and a water discharge passage. The water supply passage introduces cooling water from the body of water through a water inlet port disposed at a position that is submerged when a lower portion of the housing unit is disposed under the water. A water pump driven by the engine is used to pressurize the water for supply to the engine. The water discharge passage in turn discharges the water that has circulated within the engine from a water outlet port which usually is positioned at a submerged position. The discharge passage can be used to circulate the water to other components such as, for example, an exhaust conduit or an oil reservoir so that the water can absorb additional heat before being discharged.
The water cooling system can be provided with a pressure control valve to relieve the water pressure in the supply passage if the pressure becomes greater than a preset pressure. The pressure control valve generally is located at a portion of the supply passage and normally is connected to the water outlet port so that the excess water is discharged from the outlet port. Optionally, the excess water can merge with the water passing through the discharge passage in some arrangements. In this arrangement, the discharge passage usually is spaced apart from the supply passage and hence a relatively large pressure relief construction is necessary between the supply and discharge passages. This construction, however, is unsuitable for the outboard motors. Outboard motors are generally compactly constructed and, therefore, positioning such a connecting pathway within the housing unit of the motor is extremely difficult.
A need therefore exists for an improved water cooling system that can permit cooling water in a water supply passage to move to a water discharge passage with a compact pressure relief construction. The pressure relief construction can include a pressure control valve. The pressure control valve preferably can be easily mounted onto and/or dismounted from the housing unit for maintenance, inspection, replacement and the like.
In accordance with one aspect of the present invention, a water cooling system for an internal combustion engine comprises a housing body defining a water supply passage and a water discharge passage. The supply passage is arranged to introduce water into the system from outside. The discharge passage is arranged to discharge the water to a location outside of the system. The supply and discharge passages extend close to each other at least at one location. The housing body further defines an opening at the location through which the supply and discharge passages communicate with each other. A pressure control valve unit is disposed within the opening to connect or disconnect the supply passage with the discharge passage. The pressure control valve unit permits the water in the supply passage to move to the discharge passage when a pressure of the supply passage is greater than a preset pressure.
In accordance with another aspect of the present invention, an outboard motor comprises a housing unit adapted to be mounted on an associated watercraft. An internal combustion engine is mounted on the housing unit. The housing unit defines a water delivery passage and a water discharge passage communicating with each other through a first opening. The water delivery passage is arranged to deliver cooling water to the engine. The water discharge passage is arranged to discharge the cooling water from the engine. The delivery passage or the discharge passage communicate with a location out of the housing unit through a second opening. A pressure relief valve assembly extends through the first and second openings. The pressure relief valve assembly is arranged to allow the cooling water in the delivery passage to move to the discharge passage when a pressure of the delivery passage is greater than a preset pressure.